transition to Mutable: get rid of IO.fr
make stderr/stdout native values
fixed bug in mkEasyLet - take over case kind CWhen from enclosed expr
I/O functions for stdin/stdout, cleaned up Scanner.fr
- Removed legacies of type class Appendable, (<<) operator
- Introduced "mutable" keyword
- partial solution for qualified operators problem
  We now have 49 shift/reduce,conflicts and the right section ("oo" String.++)
  is still not working.
Fixes #36 operators can now be qualified like everything else
don't swallow superfluous QUALIFIERS before operator
basic I/O imported by default